The use of a 4D schedule as technological advancement has brought significant improvement to the planning and execution of construction projects, through visualizing step-wise construction progress, following a sequence of pre-planned activities, and finalizing a baseline schedule with necessary changes. Moreover, the application of immersive virtual reality (IVR) to create an interactive 4D BIM schedule of a planned structure has made it possible to create a detailed plan of any construction project. Because of these benefits, the use of 4D schedules and immersive virtual reality in the construction industry has increased, leading to improved planning and execution. However, past studies have given little attention to the applications of such technologies on modular projects. Thus, this research applied a 4D schedule, along with immersive virtual reality, on a modular project, and verified their benefits and effectiveness. The results showed that most of the participants who experienced a 4D BIM schedule, along with immersive virtual reality (4D/IVR), strongly agreed that it is an easy and straightforward way to visualize the project, understand the schedule, and find any errors. Moreover, while fewer than half of the participants scheduled the assembly sequence correctly with conventional schedule and 2D drawings, almost all of them sequenced the assembly successfully with 4D/IVR. Based on the findings, this research concludes that the implementation of a 4D BIM schedule, along with virtual reality technology, can enhance the fabrication and assembly performance of modules.

Modularization is a well-known construction technique where sections of the job are moved from on-site to a fabrication shop. Previously, the researchers identified the 21 most influential Critical Success Factors (CSFs) for successful modularization and quantified the degree of each CSF’s accomplishment by conducting a survey with 19 subject matter experts, and a case study with three modular projects. Through this methodology, the findings relied on the experience of experts. However, still missing from the understanding of modularization CSFs is a validation of the current degree of each CSF’s accomplishment by examining actual modular projects using a sufficient number of samples. This paper presents a comparison of CSF accomplishment degree between 25 actual sample projects (project based) and the industry experts’ survey results (experience-based estimation). The study results indicate that the industry experts made a good estimation of the current occurrence degree of each CSF. The study did identify, however, three significantly overestimated CSFs and three underestimated CSFs. The three most overestimated CSFs are Owner-Furnished/Long Lead Equipment Specification, Cost Savings Recognition, and O&M Provisions. The three most underestimated CSFs are Contractor Experience, Management of Execution Risks, and Transport Delay Avoidance. This study will help the industry to 1) better understand modularization CSFs and their accomplishment statuses; 2) achieve higher modular project performance by accomplishing the CSFs

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